System Hydraulic Retention Time Research Articles

A combined process model for wastewater treatment based on hydraulic retention time and toxicity inhibition

Hydraulic retention time (HRT), as an important parameter in the wastewater treatment process, has a great impact on water quality and energy consumption. With the rapid advances in computer technology and deepened understanding of in microbial metabolism, a series of activated sludge models (ASMs) have been developed and applied in wastewater treatment. However, ASMs simulation based on the nexus of HRT, water treatment process, water quality and energy consumption has yet to be verified. In this study, HRT was creatively linked to water treatment process variation. And a novel combined process model (CPM) was developed based on the operational data and treatment performance data from 4 full-scale coking wastewater treatment processes. In the CPM, an array of biological treatment processes were represented by setting the HRT in respective treatment units of the anaerobic-oxic-hydrolytic & denitrification-oxic (A/O/H/O) process. The relationships between HRT, effluent quality and energy consumption were systematically analyzed. Results showed that: (i) for A/O/H/O process, the HRT of first oxic (O1) reactor has a key effect on the effluent water quality and energy consumption, while the impact of the anaerobic (A) reactor HRT was limited; (ii) the O/H/O process has a clear advantage in treating coking wastewater due to the carbon removal and detoxification function of O1 reactor; (iii) the lowest energy consumption (with the total system HRT below 210 h) to meet the biological effluent quality requirements (COD = 200 mg/L, TN = 50 mg/L) is 4.429 kWh/m3. Since the CPM could effectively work out the optimal process configuration and break the boundaries between HRT and process variation, it has enormous potential to be extended to the design of other wastewater treatment processes.

Nitrogen removal mechanisms in biochar-amended sand filters treating onsite wastewater.

The performance of biochar-amended sand filters treating septic tank effluent (STE) was investigated in bench-scale columns. Softwood biochar showed higher NH4 + -N adsorption capacity (1.3mgNg-1 ), and its water holding capacity (0.57gml-1 ) was significantly higher than sand (0.26gml-1 ). Two biochar amendment ratios (10% and 30%) were selected for STE treatment in short-term (20 days) and long-term (8 months) studies. During the short-term experiment, the overall total nitrogen removal efficiency was greater in biochar-amended sand columns (94.7%-95.6%) than in 100% sand columns (71.2%) due to the additional NH4 + -N adsorption by biochar. Greater nitrification performance was also observed in biochar-amended columns (87.1%-96.3%) than in 100% sand columns (61.4%) during long-term operation when alkalinity was insufficient. The nitrification performance in biochar-amended columns resumed more quickly (<7 days) after sufficient alkalinity was amended. The density of total biomass and nitrifying bacteria in biochar-amended columns (30%) were significantly higher at all experimental stages, suggesting biochar served as a growth media for enhanced biomass growth. The alkalinity changes and STE composition fluctuation had little impact on the nitrification performance of the 30% biochar-amended sand columns. In addition, biochar surface functional groups and zeta potential changed little after long-term STE filtration. Collectively, the results demonstrated proper biochar amendment ratio (30%) could enhance the nitrification performance of sand filters treating STE by increasing the system hydraulic retention time, providing additional alkalinity for nitrification, and serving as a growth media for enhanced biomass growth.

Depuration system flushing rate affects geosmin removal from market-size Atlantic salmon Salmo salar

Common off-flavor compounds including geosmin (GSM) bioaccumulate in fish cultured in recirculating aquaculture systems (RAS) resulting in unpalatable fillets that are objectional to consumers. Most RAS facilities relocate fish from grow-out tanks to separate depuration systems with increased water flushing to remediate pre-harvest off-flavors, but certain aspects of this procedure have not been optimized including characterization of water exchange rates that effectively diminish off-flavor. To this end, a study was carried out to evaluate the effects of flushing rate and associated depuration system hydraulic retention time (HRT) on GSM removal from Atlantic salmon Salmo salar originally produced in a semi-commercial scale freshwater RAS. Twenty-six fish (5−7 kg each) were stocked into twelve replicate depuration systems operated with system HRTs of 2.4, 4.6, and 11.3-h, respectively (N = 4). Geosmin was assessed at intervals in system water and fish flesh over a 10-day feed withholding period. Waterborne GSM concentration was affected by flushing rate and associated system HRT (P < 0.05). Depuration systems operated with an 11.3-h HRT had greater waterborne GSM levels at 3, 6, and 10 days post-stocking compared to 2.4 and 4.6-h HRT. A similar trend was generally reflected in salmon flesh. Residual GSM levels were successively higher in fillets on Day 6 from depuration systems with increasingly longer HRT. Geosmin levels were greatest in salmon flesh from the 11.3-h HRT treatment on Day 10, but fillet GSM between the 2.4 and 4.6-h HRT was similar. This research indicates that lowest residual GSM is achieved in water and Atlantic salmon flesh in depuration systems with increased flushing and shorter HRT, i.e., 2.4–4.6-h under conditions of this study. Selection of optimal flushing rate to remediate off-flavor from RAS-produced Atlantic salmon may also be dictated by water and energy use metrics and site-specific water availability among other factors.

Pilot-scale anoxic/aerobic biofilter system combined with chemical precipitation for tertiary treatment of wastewater

In this study, a pilot-scale anoxic/aerobic biofilter system combined with chemical precipitation was devised and applied for the tertiary treatment of nitrogen, and post-treatment of phosphorus and residual organics in effluent from existing wastewater treatment facilities. When the system operated under a system hydraulic retention time (HRT) of 5.98 h, nitrified effluent recirculation ratio of 0.5, average methanol-supplement concentration of 23.2 mg/L, and average aluminum-sulfate concentration of 2.37 mg/L, the average concentration of BOD5, COD, SS, TN, and TP in the system effluent were 3.3, 10.4, 4.2, 6.1, and 0.43 mg/L, respectively. Despite the shorter HRT of 1.35 h in the anoxic filter packed with media, noticeable denitrification was achieved rapidly. A perfect nitrification rate was achieved and no clear deterioration in performance by chemical addition was observed. Thus, the system achieved not only outstanding nitrogen-removal performance, but also the additional removal of residual organics and phosphorus.

Renewable Energy Potential of Sewage in Zambia

This study was aimed at investigating the renewable energy potential of com- munal and municipal wastewater through methane production in biogas digesters and the use of the captured methane for energy production in biogas engines. It was conducted on biogas digesters receiving and pre-treating communal and municipal wastewater in the Zambian city of Livingstone. Wastewater inflow rates into biogas units including the wastewater turbidity, total dissolved solids (TDS), temperature, pH, conductivity and Chemical Oxygen Demand (COD) were measured during the study. And all the produced biogas was measured and combusted on-site during the course of the research. In order to know the methane content of the gas, the CO2 content in the biogas was measured with a CO2 indicator. The study showed that the predominant factor affecting the process of methane production from wastewater to the greatest extent is the COD concentration of the inflowing wastewater and not the system hydraulic retention times (HRT’s). The COD treatment levels of the tested systems ranged between 27 and 86 percent and the degree of breakdown primarily depended on the COD concentration of the influent wastewater. On renewable energy fuel production, about 3.54 kilograms of COD in each system produced a kilogram of methane. Communal wastewater was able to produce an average of 600 grams of methane per cubic meter of wastewater treated whilst municipal wastewater with less COD concentration was only able to produce about 64.5 grams of methane per cubic meter wastewater treated. With the use of a 45 kw Cummins 6 BT biogas engine, the respective wastewaters had potential to produce about 2.6 kWh and 0.1 kWh of electric energy per cubic meter of wastewater treated at a levelized cost of USD 9 cents per kilowatt-hour. Temperature also showed that it has significant effect on methane production as a degree temperature rise in the anaerobic system increased the methane production mass rate by 1.2 percent.

Evaluating the effects of prolonged peracetic acid dosing on water quality and rainbow trout Oncorhynchus mykiss performance in recirculation aquaculture systems

Peracetic acid (PAA) is an effective disinfectant/sanitizer for certain industrial applications. PAA has been described as a powerful oxidant capable of producing water quality benefits comparable to those expected with ozone application; however, the water oxidizing capacity of PAA in aquaculture systems and its effects on fish production require further investigation, particularly within recirculation aquaculture systems (RAS). To this end, a trial was conducted using six replicated RAS; three operated with semi-continuous PAA dosing and three without PAA addition, while culturing rainbow trout Oncorhynchus mykiss. Three target PAA doses (0.05, 0.10, and 0.30 mg/L) were evaluated at approximately monthly intervals. A water recycle rate >99% was maintained and system hydraulic retention time averaged 2.7 days. Rainbow trout performance metrics including growth, survival, and feed conversion ratio were not affected by PAA dosing. Water quality was unaffected by PAA for most tested parameters. Oxidative reduction potential increased directly with PAA dose and was greater (P < 0.05) in RAS where PAA was added, indicating the potential for ORP to monitor PAA residuals. True color was lower (P < 0.05) in RAS with target PAA concentrations of 0.10 and 0.30 mg/L. Off-flavor (geosmin and 2-methylisoborneol) levels in culture water, biofilm, and trout fillets were not affected by PAA dosing under the conditions of this study. Overall, semi-continuous PAA dosing from 0.05-0.30 mg/L was compatible with rainbow trout performance and RAS operation, but did not create water quality improvements like those expected when applying low-dose ozone.

Effect of volumetric organic loading rate (OLR) on H2 and CH4 production by two-stage anaerobic co-digestion of food waste and brown water

Two-stage anaerobic digestion system consisting of two continuously stirred tank reactors (CSTRs) operating at mesophillic conditions (37°C) were studied. The aim of this study is to determine optimum Hydraulic Retention Time (HRT) of the two-stage anaerobic digester system for hydrogen and methane production. This paper also discusses the effect of OLR with change in HRT on the system. Four different HRTs of 48, 24, 12, 8h were monitored for acidogenic reactor, which provided OLR of 17.7, 34.8, 70.8, 106gVS/L·d respectively. Two HRTs of 15days and 20days were studied with OLR of 1.24 and 1.76gVS/L·d respectively in methanogenic reactor. Hydrogen production at higher OLR and shorter HRT seemed favorable 106gVS/L·d (8h) in acidogenic reactor system. In methanogenic reactor system HRT of 20day with OLR of 1.24gVS/L·d was found optimum in terms of methane production and organic removal. The result of this study illustrated the optimum HRT of 8h and 20days in acidogenic stage and methanogenic stage for maximum hydrogen and methane production.

Walleye Sander vitreus performance, water quality, and waste production in replicated recirculation aquaculture systems when feeding a low phosphorus diet without fishmeal versus a traditional fishmeal-based diet

Walleye Sander vitreus is a popular sport- and food-fish in areas surrounding the Great Lakes. Walleye are mainly provided as food-fish by limited capture fisheries, but have potential for profitable production to market-size in recirculation aquaculture systems (RAS). Walleye are piscivorous with a supposed requirement for fishmeal in artificial diets, thus little information is available regarding the effects of feeding fishmeal-free diets to walleye. During this study, the health and growth performance of juvenile walleye cultured in RAS were compared between groups fed either a traditional fishmeal-based diet (FM) or a low phosphorous, fishmeal-free (FMF) diet. Water quality and waste production rates resulting from feeding each diet were evaluated. The FM diet contained fishmeal, poultry meal, soybean meal, wheat flour, and blood meal proteins; and the FMF diet used poultry meal, wheat flour, soy protein concentrate, and corn protein concentrate proteins. The only lipid source used in the FM diet was fish oil from menhaden, whereas the FMF diet used menhaden oil and poultry oil. Each diet was formulated with a protein: fat ratio of approximately 42/18. Fish (initial weight 85g fish−1) were cultured in 6 replicated RAS for 9 months, each operated with 99.9% water recycle on a flow basis, a mean system hydraulic retention time of 135days, and a mean feed loading rate of 3.5kg feed/m3 of daily makeup water. At study’s end, mean weights±standard error of fish fed the FM and FMF diets were 571±26 and 589±15g, respectively (P>0.05). Cumulative survival for both diet treatments was ≥98.5%. Average thermal growth coefficient (TGC), condition factor (CF), and feed conversion ratio (FCR) were similar (P>0.05) for the FM and FMF diets, respectively: TGC was 0.82±0.01 and 0.83±0.02; CF was 1.05±0.02 and 1.03±0.02; and FCR was 1.32±0.02 and 1.27±0.03. Water color index and UV transmittance values (P<0.05) indicated slightly clearer water in RAS where the FMF diet was fed. Total nitrogen (TN) was greater (P<0.05) in the culture water of RAS associated with the FM diet; however, TN production per unit feed was similar between treatments; 0.031±0.010kg TN/kg feed for the FM diet and 0.030±0.009kg TN/kg feed for the FMF diet. Total phosphorous (TP) concentration in the culture water of RAS associated with the FMF diet was 48% of that measured for the FM diet; TP produced per unit feed reflected this trend, 0.107±0.003 vs. 0.0049±0.006kg TP/kg feed for the FM and FMF diets, respectively. Average fillet yield (skin and scales on) of fish harvested at the end of the trial was 47–49% (P>0.05). Whole-body and fillet proximate composition was similar between treatments; however, gonadosomatic index and the ratio of omega 6: 3 fatty acids was greater (P<0.05) for walleye fed the FMF diet. This was the first study of its kind to report comparable walleye growth when feeding a specially formulated diet devoid of fishmeal and while culturing this species in RAS. Reduced phosphorous discharge resulting from feeding this fishmeal-free diet formulation increases the feasibility of meeting stringent effluent requirements and possibly reduces the capital investment required for waste treatment.

Effects of feeding a fishmeal-free versus a fishmeal-based diet on post-smolt Atlantic salmon Salmo salar performance, water quality, and waste production in recirculation aquaculture systems

The Atlantic salmon farming industry has progressively decreased the proportion of fishmeal used in commercial diets due to rising costs and sustainability concerns. A variety of alternate proteins have been identified to partially replace fishmeal; however, very little research has described the effect of feeding alternate protein, fishmeal-free diets to Atlantic salmon, particularly post-smolts cultured in recirculation aquaculture systems (RAS). Therefore, a 6-month study was conducted to compare the effects of feeding a fishmeal-free diet (FMF) versus a fishmeal-based diet (FM) on post-smolt Atlantic salmon performance, water quality, and waste production rates in six replicated RAS. Experimental diets were fed to Atlantic salmon (281±5g to begin) in triplicate RAS. Protein ingredients used in the FMF diet included mixed nut meal, poultry meal, wheat flour, and corn protein concentrate; while the FM diet contained menhaden meal, poultry meal, soy protein concentrate, and blood meal proteins. Fish oil derived from whiting fish trimmings was used in the FMF diet to establish a wild fisheries input to farmed fish output ratio of 0:1; while menhaden oil was the primary lipid source for the FM diet. Both diets were formulated with approximately 42% crude protein and 27% crude fat. Each RAS was operated with flushing rates that created an average system hydraulic retention time of 20 days (5% system volume flushed daily) and a mean feed loading rate of 3.2kg feed/m3 of daily make-up water volume. Atlantic salmon growth, survival, and feed conversion ratios (FCR) were unaffected (P>0.05) by diet. At the conclusion of the study, Atlantic salmon fed the FMF and FM diets were 1.716±0.076 and 1.720±0.065kg; cumulative survival was >99% for both; and average FCR was 0.89±0.03 and 0.90±0.02, respectively. The FMF diet resulted in greater total phosphorous (TP), carbonaceous biochemical oxygen (cBOD), and total suspended solids (TSS) mass per kg feed in the effluent (P<0.05). The FMF and FM diets produced 0.009±0.001 v. 0.006±0.001kg TP/kg feed; 0.079±0.005 v. 0.056±0.005kg cBOD/kg feed; and 0.297±0.028 v. 0.221±0.032kg TSS/kg feed, respectively. A significantly higher percentage of TSS was captured by radial flow settlers of RAS receiving the FMF diet compared to capture by settlers associated with the FM diet. Mass balance data, radial settler removal efficiency, and observations of flushed solids suggested that the FMF diet produced fecal matter with better settling characteristics. Lower TSS and true color values (P<0.05), indicative of clearer water, were measured in RAS receiving the FMF diet. Total phosphorous (most of which was dissolved) was 4 times greater in the culture water of RAS that received the FMF diet, e.g., 4.3±0.1mg/L v. 0.9±0.0mg/L for the FM Diet. This was the first research attempt to formulate a fishmeal-free diet for Atlantic salmon with this ingredient profile and one of few studies to demonstrate uncompromised Atlantic salmon performance when feeding a diet without fishmeal.

Volume ratios between the thermophilic and the mesophilic digesters of a temperature-phased anaerobic digestion system affect their performance and microbial communities

An experimental temperature-phased anaerobic digestion (TPAD) system, with the thermophilic digester operated at neutral pH and with a balanced acidogenesis and methanogenesis (referred to as NT-TPAD), was evaluated with respect to the microbial communities and population dynamics of methanogens when digesting dairy cattle manure at 15-day overall system hydraulic retention time (HRT). When fed a manure slurry of 10% total solid (TS), similar system performance, 36-38% volatile solid (VS) removal and 0.21-0.22 L methane g(-1) VS fed, was achieved between a 5-day and 7.5-day HRT for the thermophilic digester. However, the thermophilic digester achieved a greater volumetric biogas yield when operated at a 5-day RT than at a 7.5-day HRT (6.3 vs. 4.7 L/L/d), while the mesophilic digester had a stable volumetric biogas yield (about 1.0 L/L/d). Each of the digesters harbored distinct yet dynamic microbial populations, and some of the methanogens were significantly correlated with methane productions. Methanosarcina and Methanosaeta were the most important methanogenic genera in the thermophilic and the mesophilic digesters, respectively. The microbiological findings may help understand the metabolism that underpins the anaerobic processes within each of the two digesters of TPAD systems when fed dairy manure.

Comparing the effects of feeding a grain- or a fish meal-based diet on water quality, waste production, and rainbow trout Oncorhynchus mykiss performance within low exchange water recirculating aquaculture systems

Feeding a fish meal-free grain-based diet (GB) was compared to feeding a fish meal-based diet (FM) relative to water quality criteria, waste production, water treatment process performance, and rainbow trout Oncorhynchus mykiss performance within six replicated water recirculating aquaculture systems (WRAS) operated at low exchange (0.26% of the total recycle flow; system hydraulic retention time=6.7 days). Rainbow trout (214±3g to begin) were fed the GB diet within three WRAS and the FM diet within the other three WRAS for 3 months. Feeding the GB diet resulted in significantly greater total ammonia nitrogen (TAN) throughout the study, as well as significantly greater total suspended solids (TSS) and carbonaceous biochemical oxygen demand (BOD) over the greater part of the study. Greater counts of fine solids (2–30μm) were associated with the GB diet. Water clarity was improved for the GB diet as reflected by significantly reduced true color and increased ultraviolet transmittance. Total and dissolved phosphorous, as well as the daily mass captured per kg feed of total phosphorous were significantly lower within the effluent associated with the GB diet. The daily mass of total nitrogen and TSS captured per kg feed and discharged from each WRAS was equal between diets, but waste load among three discharge flows varied. Waste removal efficiency across unit processes was similar between diets, with the exception of solids removal efficiency across the microscreen drum filter and the radial flow settler, which was generally lower for the GB diet. Rainbow trout growth, feed conversion, condition factor, and survival were similar between diets. Survival was 99.5±0.2% for both diet treatments. Skin-on fillet yield and whole-body protein levels were significantly greater at the end of the study for trout fed the GB diet. Overall, the GB diet evaluated during the present study proved to be a viable feed option for use within a low exchange WRAS. However, further refinements to grain-based diet formulations and/or use of ozone to improve water quality when feeding GB diets within low exchange WRAS could be beneficial.

Treatment of a slaughterhouse wastewater: effect of internal recycle rate on chemical oxygen demand, total Kjeldahl nitrogen and total phosphorus removal

This study investigated the ability of an anaerobic/anoxic/oxic (A2/O) system to treat a slaughterhouse wastewater. The system employed two identical continuous-flow reactors (10 l total liquid volume each) running in parallel with the main operational variable, being the internal recycle (IR) rate. The chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN) and total phosphorus (TP) performance was evaluated as the IR flowrate was increased from a Q of 15 l d−1 to 4Q at a system hydraulic retention time of 16 h and a solids retention time of 10 d. The COD:TKN and COD:TP ratios were 8.2:1 and 54:1, which supported both nitrogen and phosphorus removal. For all IR multiples of Q, the COD removal was in excess of 90%. The TKN removal showed a modest improvement (a 4–5% increase, depending on the dissolved oxygen (DO)) as the IR doubled from Q to 2Q, but no further increase was observed at the 4Q IR rate. The TP removal reached its optimum (around 85%–89% (again depending on the DO)) at the 2Q rate.

Abnormal swimming behavior and increased deformities in rainbow trout Oncorhynchus mykiss cultured in low exchange water recirculating aquaculture systems

Two studies were conducted to evaluate rainbow trout Oncorhynchus mykiss health and welfare within replicated water recirculating aquaculture systems (WRAS) that were operated at low and near-zero water exchange, with and without ozonation, and with relatively high feed loading rates. During the first study, rainbow trout cultured within WRAS operated with low water exchange (system hydraulic retention time (HRT)=6.7 days; feed loading rate=4.1kg feed/m3 daily makeup flow) exhibited increased swimming speeds as well as a greater incidence of “side swimming” behavior as compared to trout cultured in high exchange WRAS (HRT=0.67 days; feed loading rate=0.41kg feed/m3 daily makeup flow). During the second study, when the WRAS were operated at near-zero water exchange, an increased percentage of rainbow trout deformities, as well as increased mortality and a variety of unusual swimming behaviors were observed within WRAS with the highest feed loading rates and least water exchange (HRT≥103 days; feed loading rate≥71kg feed/m3 daily makeup flow). A wide range of water quality variables were measured. Although the causative agent could not be conclusively identified, several water quality parameters, including nitrate nitrogen and dissolved potassium, were identified as being potentially associated with the observed fish health problems.

Effect of mixture ratio, solids concentration and hydraulic retention time on the anaerobic digestion of the organic fraction of municipal solid waste

This paper describes how the degradation of the organic fraction of municipal solid waste (OFMSW) is affected through codigestion with varying amounts of return activated sludge (RAS). Solid waste that had its inorganic fraction selectively removed was mixed with RAS in ratios of 100% OFMSW, 50% OFMSW/50% RAS, and 25% OFMSW/75% RAS. The total solids (TS) concentration was held at 8% and three anaerobic digester systems treating the mixtures were held (for the first run) at a total hydraulic retention time (HRT) of 28 days. Increasing amounts of RAS did not however improve the mixture's digestability, as indicated by little change and/or a drop in the main performance indices [including percentage volatile solids (VS) removal and specific gas production]. The optimum ratio in this research therefore appeared to be 100% OFMSW with an associated 85.1 ± 0.6% VS removal and 0.72 ± 0.01 L total gas g(- 1) VS. In the second run, the effect of increasing percentage of TS (8, 12% and 15%) at a system HRT of 28 days was observed to yield no improvement in the main performance indices (i.e. percentage VS removal and specific gas production). Finally, during the third run, variations in the total system HRT were investigated at an 8% TS, again using 100% OFMSW. Of the HRTs explored (23, 28 and 33 days), the longest HRT yielded the best performance overall, particularly in terms of specific gas production (0.77 ± 0.01 L total gas g(-1) VS).

Heavy metal and waste metabolite accumulation and their potential effect on rainbow trout performance in a replicated water reuse system operated at low or high system flushing rates

A six-month trial was conducted to compare the effects of high and low make-up water flushing rates on rainbow trout performance and water quality in replicated water reuse aquaculture systems (WRAS). Six identical 9.5m3 WRAS, containing a single 5.3m3 tank and operated at a total recirculating flow of 380L/min were stocked with 1000 rainbow trout each (133±1g). Three WRAS were operated at high flushing rates (2.6% of total flow) and three were operated at low flushing rates (0.26% of total flow), providing system hydraulic retention times of 0.67 and 6.7 days, respectively. During a one-week period when fish were at maximum feeding (i.e., mean feed loadings of 0.53 and 5.3kg/m3 make-up water flow high and low make-up conditions, respectively) and maximum densities (80kg/m3), water samples were collected across all unit processes. All typical water quality parameters measured at the culture tank outlet during this week were significantly different between treatments, except for dissolved oxygen, carbon dioxide, and temperature, which were controlled. Within the low exchange WRAS, total suspended solids (TSS), carbonaceous biochemical oxygen demand, total ammonia nitrogen, un-ionized ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, dissolved organic carbon, particle counts, true color, and total heterotrophic plate counts were significantly greater, whereas UV transmittance (%) and alkalinity were significantly reduced. Of these parameters, TSS, fine particles, and heterotrophic bacteria counts were the only parameters of concern within the low exchange WRAS. The potential impacts of each water quality constituent are discussed. Element analysis indicated that concentrations of nine metals were significantly greater within the low exchange WRAS. The highest metal concentrations measured at low exchange were within safe recommended limits, with the exception of copper (0.037–0.056mg/L), which could have reached chronically toxic levels. Although cumulative mortality was relatively low for all WRAS, a linear trend between copper concentration and mortality was evident. The highest mortality, which occurred within a low exchange WRAS, coincided with the highest copper (0.056mg/L); and the lowest mortality, which occurred within a high exchange WRAS, coincided with non-detectable copper levels. A comparison of survival between treatments bordered significance, 99.5±0.1 and 98.9±0.4% for the high and low exchange WRAS, respectively. There was no significant difference in rainbow trout weight at the conclusion of the study, i.e., approximately one year post-hatch: 1401±23 and 1366±33g for the high and low exchange WRAS, respectively. There were no differences in thermal growth coefficients or feed conversion ratios between the high and low exchange treatments. Rainbow trout condition factor was significantly greater within the low exchange WRAS.

Simultaneous Nitrification and Denitrification with Anoxic Phosphorus Uptake in a Membrane Bioreactor System

The performance of an innovative membrane bioreactor (MBR) process using anoxic phosphorus uptake with nitrification and denitrification for the treatment of municipal wastewater with respect to operational performance and effluent quality is addressed in this paper. The system was operated at steady-state conditions with a synthetic acetate-based wastewater at a hydraulic retention time (HRT) of 12 hours and on degritted municipal wastewater at a total system HRT of 6 hours. The MBR system was able to achieve 99% biochemical oxygen demand (BOD), chemical oxygen demand (COD), and ammonia-nitrogen (NH4(+)-N); 98% total Kjeldahl nitrogen (TKN); and 97% phosphorus removal, producing effluent BOD, COD, NH4+-N, TKN, nitrate-nitrogen, nitrite-nitrogen, and phosphate-phosphorus of <3, 14, 0.2, 0.26, 5.8, 0.21, and <0.01 mg/L, respectively, at the 6-hour HRT. The comparison of the synthetic and municipal wastewater run is presented in this paper. Steady-state mass balance on municipal wastewater was performed to reveal some key features of the modified MBR system.

Combined Removal of Carbon and Nitrogen in an Integrated UASB-Jet Loop Reactor Bioreactor System

An innovative anaerobic–aerobic integrated bioreactor system consisting of an upflow anaerobic sludge blanket (UASB) and a jet loop reactor was developed to investigate the feasibility of combined removal of carbon and nitrogen for a low-strength wastewater at different hydraulic retention times (HRTs) and recycle ratios. Total chemical oxygen demand (COD) removal of the integrated system increased from 87 to 92%, at a combined system HRT of 44 h , when the recycle ratio was increased from 100 to 400%, respectively. Denitrification efficiency of the integrated system increased from 49 to 86%, at all HRTs, when the recycle ratio was increased from 100 to 400%. The integrated system, on average, achieved more than 78% of total nitrogen at all HRTs. Nitrogen content of the biogas produced from the UASB reactor increased with increase in recycle ratios while the methane content exhibited a reverse trend, irrespective of the HRTs. Sludge volume index of the UASB reactor increased from 15 to 42 mL∕g total suspe...

Performance assessment of a UASB–anoxic–oxic system for the treatment of tomato-processing wastes

An upflow anaerobic sludge blanket (UASB)–anoxic–oxic system was used to achieve biochemical oxygen demand, NH4 and total suspended solids (TSS) criteria of 15, 1 and 15 mg dm−3 at 1.17 days of system hydraulic retention time during treatment of tomato-processing waste. The incorporation of an anoxic tank was found to affect the improvement in sludge-settling characteristics, as reflected by about 25–33% reduction in the sludge volume index, along with final effluent TSS and soluble biochemical oxygen demand concentrations of 13 and 9 mg dm−3, respectively, which met the discharge criteria. Despite incomplete denitrification, sludge settleability was very good (sludge volume index < 60 cm3 g−1) owing to reduction in volatile suspended solids/TSS ratio from 0.75 to 0.6 as a result of higher alkalinity in the UASB effluent. Also in this study, phosphorus release was observed in the anoxic tank, predominantly due to abundance of acetic acid in the UASB effluent. A phosphate release of 5.4 mg P dm−3 was observed in the anoxic tank with subsequent P uptake in the following aerobic stage. Copyright © 2006 Society of Chemical Industry

EVALUATION OF TWO-STAGE ANAEROBIC SEQUENCING BATCH REACTOR SYSTEMS FOR ANIMAL WASTEWATER TREATMENT

Anaerobic treatment of screened swine and dairy manure was studied in the laboratory with two-stage anaerobic sequencing batch reactor (ASBR) systems. The effects of anaerobic treatment on odor control in subsequent manure storage units were evaluated. One thermophilic (55°C) mesophilic (35°C) system (II) was evaluated against one mesophilic (35°C) mesophilic (35°C) system (I) at a system hydraulic retention time (HRT) of six days and four volatile solid (VS) loading rates (1, 2, 3, 4 g/L/day). Generally, anaerobic digestion under all the test conditions resulted in higher solids reduction in swine manure than in dairy manure. The thermophilic-mesophilic system had a better performance in treating dairy and swine manure with 6 to 15% more VS removal than the mesophilic-mesophilic system. The headspace gas analysis results using manure storage jars showed that both systems were effective in reducing the generation of odorous sulfur gases during storage. The untreated dairy and swine manure exhibited strong offensive odors with high hydrogen sulfide (H 2 S) and mercaptan concentrations detected in the headspaces of storage jars. The anaerobically treated manure, however, showed minimal residual odors while in many cases, H 2 S and mercaptans were not detectable. With the consideration of its better capability for destructing fecal bacteria in animal manure, the thermophilic-mesophilic ASBR system is more advantageous than the mesophilic-mesophilic ASBR system for treating animal manure. However, the higher energy requirement for heating the reactors in the former system needs to be considered when selecting thermophilic vs. mesophilic anaerobic digestion systems. Keywords. Anaerobic digestion, Anaerobic sequencing batch reactors, Odor control, Dairy, Swine, Manure.

Treatment of dairy wastewater with two-stage anaerobic sequencing batch reactor systems — thermophilic versus mesophilic operations

A two-stage anaerobic sequencing batch reactor (ASBR) system was studied in the laboratory to evaluate a temperature-phased anaerobic digestion process for dairy wastewater treatment. The temperature-phased anaerobic digestion system incorporates thermophilic digestion and mesophilic digestion processes into one system which has the potential to offer the benefits of high digestion rate, fecal bacteria destruction, process stability, and favorable economics for animal wastewater treatment. Two thermophilic (55°C)-mesophilic (35°C) systems (II and III) were evaluated against one mesophilic (35°C)-mesophilic (35°C) system (I) at two system hydraulic retention times (HRTs) (3 and 6 days) and five volatile solids (VS) loading rates (2, 3, 4, 6 and 8 g/l/day). The three systems were designed with different first- and second-stage volume ratios: 1:4 for systems I and II and 1:2 for system III. The effects of temperature configurations and volume ratios between the two stages, HRTs, and VS loading rates on the performance of the two-stage ASBR system were studied. A relatively high solid retention time (SRT) of 13–18 days was achieved at both 3- and 6-day HRTs for all three systems. The performance of each system depends on the HRT and the VS loading rate. All three systems at the 3-day HRT deteriorated when the VS loading rate reached 6 g/l/day. The total solids (TS) and volatile solids (VS) removals were similar for 3- and 6-day HRTs at the VS loading rates of 2, 3 and 4 g/l/d. For the same VS loading rate in the range of 2–4 g/l/day and the same first- to second-stage volume ratio (1:4), the VS removal and specific methane production rate of the thermophilic-mesophilic system (II) were 43.8–44.1% and 0.41–0.82 l/l/day for 3-day HRT, respectively, and 37.1–38.9% and 0.34–0.72 l/l/day for 6-day HRT, respectively, which are higher than the VS removal and specific methane production rate of the mesophilic-mesophilic system (I) (29.3–30.2% and 0.27–0.56 l/l/day for 3-day HRT, respectively; 26.1–29.1% and 0.27–0.48 l/l/day for 6-day HRT, respectively). With the thermophilic-mesophilic system, the 1:4 ratio for the first- and second-stage reactors yielded better solids removals and methane production rate than the 1:2 ratio. Both thermophilic-mesophilic systems were found to be more effective in destroying the total coliforms present in the wastewater than the mesophilic-mesophilic system. As far as solids removal, biogas production, and coliform bacteria destruction are concerned, thermophilic-mesophilic systems are recommended over the mesophilic-mesophilic systems. However, the increased heating energy requirement of the former system needs to be considered when comparing the economics of these two treatment systems.